1. Technical Field
The present invention relates to a projection display system, which magnifies an image of an image display element to project the same onto a surface of a screen, etc. to display the image, and more particular, to a projection display system suited to display an image on a large screen.
2. Related Art
Various kinds of color image projection display systems has been already known and put to practical use, which magnify and project an image of an image display element onto a screen (projection plane) through a projection optical unit composed of a plurality of lenses. Such display systems are required to get a magnified image having a sufficiently magnitude on a screen without distortion. In order to realize this, as described in, for example, JP-A-5-134213 and JP-A-2000-162544, there has been already known a projection unit or an optical system, which shifts a projection plane in a perpendicular direction in relation to an optical axis of a projection system, magnifies and projects an image onto a screen in an oblique direction with the use of an additional optical system, which is arranged to be inclined at a predetermined angle to the optical axis of the projection system. The additional optical system (afocal converter) referred herein to is an optical system acting to convert a magnitude of a projection image and serving to correct/decrease distortion of the image caused by projection onto a screen in an oblique direction to obtain a rectangular-shaped projected image.
There has been also known, for example, in JP-A-2004-157560, a reflection type imaging optical system, which magnifies and projects an image of a display element onto a screen (projection plane) with the use of a plurality of reflecting mirrors (reflection type optical elements) instead of the lenses (transmission optical elements).